Stacked Yagi Antennas

This article was obtained from VE3GK experiences, constructing and designing full size, single band stacked yagi antenna arrays, special rotating, electric powered, telescoping towers and rotators. All the test results are from first hand experiments. VE3GK kept a record of these experiments and construction details and offer them for your interest.

HISTORY

I started out in amateur radio with wire antennas. Directional antennas were next and I erected a commercial tri-band antenna, tower and rotator. Another amateur, nearby, used a wide spaced mono-band 20-meter beam, which blew me away every time. From this experience I felt that my set up left a lot to be desired.

I started with a 5-element 20-meter mono-band yagi on a 48-ft boom. As the years passed several different home made full size long boom multi-element yagis were mounted singly and in the stacked array configuration on modified lattice towers. These towers were modified to rotate to accommodate the stacked array set up.

Antennas were eventually mounted on two home designed and home made continuous heavy duty telescoping rotating tubular steel towers. Stacking separation distances and overall height above ground experiments were conducted on the large tower on a small mountain 65 miles south of Ottawa at our summerhouse. In the winter time, in Ottawa, I experimented with a smaller, 75 ft rotating telescoping home made tower. The tower is designed for continuous operation. I try to lower the thing out of sight in the trees, in its parking position, every time I leave the shack for over 30 minutes or so. Out of sight, out of mind, for my neighbors. (My stealth equation HI) This tower also tilts over electrically with a permanent 5 in diameter, 12 ft high gin pole mounted in the cement base.

This in a neat arrangement for ease of antenna installation and adjustment. With the exception of the commercial tri-bander all of the hardware presented in this paper is home constructed and home designed.

My present radiating system is a 20- meter, four over four stacked array with yagis on 40-foot [12m] booms at the summer place. All of my mono-band yagis use odd spacing with a close coupled first director and placed 0.1- wave length in front of the driven element. The top beam is usually at 90-feet [27m] and the bottom one at 42-feet [12.6m] when in the stacked arrangement.

Two 4 element 40 foot boom yagis fed in phase. When up, one at 95 feet and the other at 38 feet. When nested, one at 28 feet and the other at25 feet above ground. Nesting happens automatically in wind gusts above 60 kph, when I leave the property and at the end of operating hours or evening shut down. The time travel is 7 minutes 40 seconds up or down. There is a manual crash descent, (Letting the tower free wheel down), of 30 seconds in case of a sudden storm. The estimated tower weight is 2.5 tons, 2 tons are active when the tower is under power. This weight is supported by the lift cables (16 tons capacity) at all times. The tower is freestanding, telescopic, rotating, remote control, double safety devices on all tower sections and lift cables. Automatic end stops on the tower extension and nesting positions. Also safety devices on full cw and ccw rotation parameters. The hoist and rotator parameters are monitored on close circuit tv using two tv cameras. Audio feed-back information is feed back with a baby monitor.

The following conclusions are based on my own full size live tests, and are to be weighed accordingly.

I want to thank those people who helped me with all the antenna tests. I especially want to thank those who were patient enough not to shoot me off the top of the towers during the tests.

NOTE:

In the commercial antenna market their seams to be an emphasis on working as many bands as possible on one boom with mediocre results on any one band. Don’t believe the claims that multi-band beam antennas exist that can compete with antennas designed for one band. Log periodic beam antennas are not high gain antennas, they are wide band coverage devices that have gain compared to that of a 3 element beam antenna , designed for one frequency.

In Ottawa I use a commercial 5-element tri-band yagi on the telescoping, rotating, 75-ft tower. This fall and Winter it is my intention to stack another identical tri-band yagi on the tower at 25 ft. These experiments are possible because I can adjust the stacking separation distance for 10 and 15 meters. I will not be able to stack on 20 because the top beam is not high enough. (The tower is higher but not capable of supporting the weight of the heavy tri-bander on the top section

MEASURING GAIN WITH REFERENCE TO A DIPOLE:

Measuring gain with absolute certainty is very difficult because of all the variables. However, as far as I can determine the gain of the present 4X4 array is about 11 DBD. [db reference to a Dipole]. The single 40 ft long 4 element beam is responsibly for about 8-DBD and the stacks at 3/4 wave separation with the top one at 90-ft add another 3-DBD to the results for a total of 11-DBD.

Antenna gain is measured with reference to power gain. For example; when the power of an amplifier is doubled from 100 watts to 200 watts, the resulting gain would be 3 DBP; the "P" stands for the previous condition or situation. This 3 DB factor comes from the formula that states that power and therefore, antenna gain is equal to 10 times the log, to the base 10, of the new situation divided by the old situation. Here the new power divided by the old power equals 2, the log of 2 equals 0.3 and 10 times 0.3 equals 3, 3DBP gain.

A practical antenna gain measurement could be done as follows: Mount a 20m-reference dipole and oriented it at the proper height, far enough away to de-couple any interaction with the test array. Apply 100 watts to a dipole as indicated on a good wattmeter such as the BIRD 43. Have another amateur, at least one skip distance away, and note his "S" meter reading. Then apply power to the test array and reduce the power and one should get the same "S" meter reading with lower power. This operation has to be done very quickly to out-run any QSB on the band. In my case with the present 4x4 array I am able to get the same "S" meter reading with only eight watts. Divide this 8-watt power level into the 100-watt reference and the results will be approximately 12. The log of 12 is about 1.1 and 10 times 1.1 equals 11, 11DB. Arriving at an honest DBD gain factor is very simple.

(17. probably the limit for effort and gain return for HF collinear stacks)

Simon, OH8OS, in Finland, had a 6X6 by 6X6 by 6X6, 60-ft booms

horizontal separation of 60-ft, Top antenna over 200-ft

above ground. A total of 36-el. Approx. Gain ??-DBD

WOW! Is this a 20-meter monster antenna array or what?

Note: A dipole would have to be driven with a bunch of kilowatts of power to equal the output from the OH8OS array with bare-foot power. All that power into a dipole with no receiver gain. WOW! For instance, you would have to drive a dipole with about 700-watts to equal the output power of a 204-BA, Hygain 4-element beam with only 100 watts drive power. Can you imagine the legal power limit to the array OH6OS used, don’t fry, oh sorry fly, in front of the sucker if Simon were to sneezed into the microphone. HI.

GAIN

GAIN REALLY HARD TO COME BY:

LONG BOOM SINGLE BAND YAGIS:

When a person asks "what’s that big aerial thing doing up there..EH ?" I always say. "If you think the aerial is big, you should see the size of the TV set."

"That’s not QSB man. It’s the wind blowing my antenna around." My 7-element on a 65-ft [19.5m] boom had a very narrow beam pattern. It was also big enough because it blew up and over the top of the tower in a January ice-wind storm in 1975, more later. It was my first "JC" antenna. People would drive by and fall off the road. Other amateurs would drive by with their spouses and suggest a tri-bander! If you hear a big signal break the pile up, listen to the description of that station. I can assure you, a lot of time, money and effort has gone into the signal. Some people rationalize the strength of a very strong signal by assuming high-power. I’m accused of running over power. I sometimes say, "I’m running illegal antennas".

Note: the reflector for this ve3gk 6 element 20-m yagi is sitting on the ground at the base of the tower

This antenna was used as a reference source for my 5X5 and 4X4 stacked arrays for a period of time. My QTH was about 6 KM away.

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Ve3gk, doing his "walk the boom trick" in my younger stupid days! Near home brew 60-ft 20-m yagi at 90-ft

VE3GK antennas.....

Over the years, there has been some big, long boom yagis up. The photo to the right shows W4GNR sitting at the top of his 140 ft high tower on the 120 ft long boom 20 meter yagi up at 140 ft. I remember a 20-meter yagi in the early 1960`s in the mid west USA, a real monster. The thing had 12 elements on a 150-foot [45m] boom up 150-feet [45m]. A real cannon, it surely would have been a sight to behold. With what we know now this antenna would have worked more efficiently with fewer elements. It was also up too high for in close DX such as Europe because of its very low launch angle.

Remember; gain from a long boom single band Yagi comes from the focusing of the frontal lobe by the extra director’s way out on the boom. From my experience, when you have a long boom the forward gain and the front to back ratio is one and the same because of the refined frontal pattern.

The take off angle to the horizon is mostly related to the antenna height above true flat ground for single yagis. If one gets involved with a stacked system its a different ball game. A tacked system modifies the take off angle with startling results. From my experience, it eliminates one skip distance to Europe. My advice is that you do the best you can with what you have and go for it. As a rule, single antennas will work really well at one wavelength above ground. The antenna performance will really come alive at 1.5 wave-lengths above ground (99-ft for 20 meters). You will be amazed with your new signal. If the antenna is placed much higher the in-close path to Europe from North America will suffer. Asia and the Indian Ocean area will be better so you have to make a choice. The next paragraph could solve this Delrina.

THE TELESCOPING TOWER:

With a remote controlled, telescopic tower, one can experiment with the launch angles for changing DX openings. As far as I can tell the towers that I have built are the only ones that have the ability to fully rotate and are free standing. Also, most telescoping towers are not designed for continuous height adjustments so it’s not feasible to run the experiments. The towers that I have are specially designed to perform these tasks. The large 118-ft tower at my DX location at the summerhouse is designed to modify the take off angle for the ideal skip condition. I don't know of any company offering this tower commercially.

The 100 ft tower on it's way

On a lighter note, with a telescoping tower you can let the tower grow on the neighbor’s say a foot every day HI. Maybe make the hoist system ultra fast about 1-ms for full up or full down in the trees. You could put a neighbor sensor on the thing and when they look out the window down it comes. "What tower, what antenna? EH" All kidding aside, its interesting to be able to adjust the take off angle for different areas and times of the day.

My second 80-ft (24m)-telescoping tower in Ottawa tilts over. This is fantastic for the initial erection and flexibility for future modifications. Most importantly, is that initially you don’t have to have a high profile crane come in. That’s "high profile City." Neighbor: "You know when that BIG CRANE came over to your yard and you had the big erection, well ever since that thing went up my washing machine has been over sudsing!"

BAND WIDTHS AT THE HALF POWER

From my experiments the yagis that I constructed had wide low reflected-power bandwidths that usually cover the entire band with less than 2 percent reflected power. I am fully aware of the theory that a narrow bandwidth results in a larger gain factor. However, I seam to have more than enough gain from my practical experiments and the ability to roam the entire band with low vswr in very appealing to me. VSWR curves above 1.5 to 1 on my long yagis were usually occurred outside the band on 20-meters. The half power points were awesome at plus or minus < 30 degrees. Half power beam density points are those points that are out to the sides of the beam pattern and are 3-DB down with reference to the maximum density of the middle of the beam pattern.

There are certain construction techniques used when building short yagis that seam to indicate that one can tune either for maximum front to back or maximum forward gain. Usually, the frontal lobe will be skewed and the forward gain suffers a little. I should not comment further because I have real problems relating to antenna things that I have not experienced first hand. I have always worked with long boom yagis and in this situation one works both on the front to back and with the focussing of the energy in the frontal lobe. Elements, far out on the boom, focus the energy. The gain comes from the missing density from the mods in the rear lobe by the reflector and the side’s lobes by the directors and more importantly the long boom. From these experiences, I find it very difficult to separate the front to back with the forward gain. Again, I feel the forward gain of the array is directly related to the re-arranged flux density both on the back and the sides.

THE NEIGHBOR ANXIETY INDEX:

Large antenna arrays are prone to all sorts of problems, not the least, the anxiety level of all the neighbors. My large telescoping tower with the stacks is mounted in the trees on the edge of a large lake in eastern Ontario. This QTH is the highest area in eastern Ontario. About a mile of water separates my QTH from a large campsite across the bay. I ventured over their one day and was asked, "what do you think that strange structure is across the bay?"... "The thing is there sometimes, and sometimes it’s not. WOW! .. Very strange." I said, "I thought it was some sort of secret government installation, an area to be avoided at all costs." When people bring your antenna system up in conversation, just say "thank you, thank you," and tell them that the thing will protect them from lightening storms, "just my little contribution to the well being of the neighborhood."

Watch for the gun barrels out the windows. Maybe you should only climb the tower at night in the city.

THE PUBLIC RELATIONS CAPER:

On a more practical note, last year I used my snow blower to clear several neighbors’ lane ways while they were at work. HI

Start with the popular, Hy-Gain, 204BA, a 4-element Yagi on a 26-ft boom and double the length to 52-ft, [15.6m]. You should only add one extra director for a total of 5-elements in this project. (Obviously, I think the present design of the 204BA is over-populated with elements.) However I still admire the design of this antenna because it’s a strong competitor on band. I know this sounds odd but for what it’s worth I think the 204BA is actually a 3-element beam with an extra director. The first director is a foot [0.3m] longer than the other directors and is always placed 0.1-wavelength (7-ft) [2.1m], in front of the driven element on 20-m. Some amateurs have called it the phantom element. I use this odd, close-coupled, over size, director design on all my yagis and feel that the results are really worthwhile.

The spacing on the 205GK, 5-element were, starting from reflector end: 12-ft [3.6m], 7-ft [2.1m], 15-ft [4.5m], and 18-ft [5.4m]. The element lengths stay the same as the 204BA and the last director is 2 inches [5cm] shorter than the one before it. I also substituted an OMEGA match for the original 204BA-matching network. Complete details are in another chapter. Wait until you try this new super 205GK modification to make the 204BA into a 5-element on a 52-ft [15.6m] boom. This antenna will astound you. You can throw out the theoretical 2-DBP-gain figure. It seemed most of the time to be around two "S" units. I remember a five element made by a well-known beam manufacturer on a 46-ft boom that outperformed their 6-element on the same boom. However, the company made the 6-element available for those who wished to say they were running six elements. Some beams have several driven elements to cover the bandwidth. My long yagis designs cover the whole band with lots to spare, more later. I understand that the antennas should work better at some point in the band, but I don’t see any change in performance over the entire band. Five element yagis were a passion of mine in the 70`s and 80`s and I built several of them. The largest one was on a 53-ft (17.6m) boom. I also built a 7-element on the 63-ft (21m) boom, and fun learning project. I know, I know, 7-elements on this length of boom was too crowded, the boom should have been about 100-feet [30m] long, but you learn as you go. I describe these home brew beams in other chapters.

THE THREE ELEMENT YAGI:

I have to say that I have never had any real success with a 3-element yagis design. Oh, I got them to work but they didn’t have that magic touch in a crowd, even when I stacked them. I think all mono-band beams need the magic short-coupled first director, so there has to be a minimum of 4-elements. So I guess the three-element beam for 20 meters is not in the big game. Remember if you don’t agree with my observations turn the dial, HI. From my point of view, the 4-element single band is the most popular competitive beam in use today on 20-meters.

DO NOT READ THIS PARAGRAPH:

You know it appears to me a lot of people are just relying on other so-called experts to do they’re experimenting for them. Some of the gain figures are really inflated as far as my experiments dictate. I hear that there is a magic 2-element on 20 meters on an 18-ft boom, crowded with other bands, that has a 10-DBD + gain figure. Must be some magic here. Think about it, would operating 100 watts to the thing be the same as running 1100 watts to a dipole in the same spot? NOT!!!!!!!

"Let me run your design by my computer program and see if it’s a good design". This is right after I have broken a force 10 or 12 pile-up with 200 watts bare foot on the first call into Asia. "No..., you run your program by my design and see if it measures up.

Because of gusty winds and heavy ice in some areas, the life expectancy of large beams is short. The big guys require special towers and extra special rotating systems. I used to rotate the big beams with long drive tubes with the rotator mounted at the base of the tower at ground level. Steel wires ran down the side of the tower to show the beam heading independent of the backlash of the long tube. The main reason for the tube was to eliminate the need for the tower to handle the severe torque power from the long booms in heavy winds. Is it ever neat to be able to get at the rotator at ground level, especially in the dead of winter? As an added torque absorber, I over-lapped two diameters of the torque tube just above the rotator. Then I welded a large automobile front-end suspension coil spring onto each tube so that the spring was in series with the drive system. This "spring" idea came from Gib, VE3BGX in Ottawa.

Special rotators had to be designed for the new rotating towers. One design used four VEE belts in parallel. (I think this was the best design). However, the belts had a short life span because of the proximity to oil and grease. Because the tower had to be lifted out by crane in order to change the belts, a second method was designed using small diameter steel cable. The cable design was not unlike the winch method mounted on its side. This is the method I use at present on the large tower. The smaller 1.5 ton tower uses a new design using a linear drive consisting of a 30 inch, [75CM], 3/4, [2-CM] inch diameter, 10 turns per inch threaded rod driven by a one third horse power electric motor. This new design does not require an expensive gearbox reduction drive assembly. Also this rotator could be located at ground level and drive cables could run several hundred feet to the top of the tower. This cable rotating method also relieves the tower of any responsibility for torque restraint. A heavy-duty relief spring is installed in series with the drive cable to relieve any bumps in torque due to gusting winds. The rotator has more than enough power to rotate the largest 80-M beam -tower at a fraction of the cost. There are no expensive gears to strip and the unit is self-braking. A triangle tower could be rotated this way quite easily because the wire winch drive can’t tell the difference between rotating a circle or a triangle. One would have to re-calibrate the beam indicator because of the difference in the diameter from the point of the triangle to the side of the triangle. The other option would have steel drum welded to the tower so that the radius of the tower remain constant.

THE NEW ERA OF THE SHORT BOOM YAGI ANTENNA.. MAGIC GAIN ANTENNAS?

Don’t let anybody claim they have a magic antenna on a shortened boom, with less elements, that works as good as or better than a longer one because they are just fooling themselves and trying to fool you. Logic dictates that a boom with other elements for other bands on it will not work as well as a boom dedicated to one band.

THE BRONTOSAURUS GUN:

REMEMBER.....Combine the gain from several long boom yagis in the stacked array and you have a real brontosaurus gun.